I think Union bindings are pretty good, but I'm a big fan of canting footbeds, which Union doesn't seem to offer so I could never use them for long. I think Romes canting options are perfect for me, but overall I think Rome is like Union, pretty good. As much as I hate giving my money to Burton, I've always been impressed with their bindings more so than Union or Rome.
It's great to live in a free world.
Bottom line, all 3 of these are great bindings. Here are some of the main differences in my OPINION.
Burton - Unibody baseplate.
Rome & Union - Adjustable heelcups.
Union & Burton - Anatomic baseplates.
Rome - Anatomic everything, except the actual nylon baseplate is symmetrical.
Regarding canting - We've been working on this for a while, and will have canting on a model or 2 next year. The reason we haven't pursued it is simply because none of the team guys have wanted it. I think until we see a significant amount of guys asking for it, it's not going to be something we offer across the line. Out of 100 people we give bindings to, I've heard the request from maybe 4. The reason for this is probably because non of them ride huge stances. It's a non issue.
Back to work. Just wanted to share my thoughts.
Have a good day!